1. Field of the Invention
This invention relates to a polyimide silicone resin effectively utilizable for uses in, e.g., prevention of corrosion of liquid-crystal display panel electrodes and surface protection of wiring component parts of semiconductor devices and printed circuit boards, and also relates to its solution composition and a polyimide silicone resin film.
2. Description of the Prior Art
Room temperature-vulcanizable (RTV) silicones are widely used in protective materials for electrodes of liquid-crystal display panels, the electrodes being formed of, e.g., ITO (indium tin oxide). However, as display devices have been improved in performances in recent years, specifically, their panels, weights and thickness have been made larger, lighter and thinner, respectively. Also, as liquid-crystal display panels have become used in a wide range of purposes, severer properties have become required for electrode protective materials. Accordingly, it has been sought to bring out more highly reliable electrode protective materials.
Meanwhile, polyimide silicone resins have energetically been researched and developed in recent years. They, however, are usually only known as those of a type which can be diluted in a high-boiling solvent or as those of a type which can be used as solutions in the state of polyamic acid (i.e., the precursor of polyimide), i.e., solutions of polyamic acid silicone resins. In the case of the polyimide silicone resins of the type which is diluted in a high-boiling solvent, the solvent must be removed at a high-temperature to effect curing in order to obtain the desired films. Hence, such resins are not adaptable as electrode protective materials for liquid-crystal display panels not resistant to high temperatures. Similarly, the polyamic acid silicone resin solutions must be treated at a high temperature of 200xc2x0 C. or above in order to effect imidization; thus, in this case, too, the resins are not suitable as electrode protective materials for liquid-crystal display panels.
The electrode protective materials are also required not to impart any stress to the display panels. However, conventional polyimide silicone resins can not endow films with elasticity, compared to room temperature-vulcanizable (RTV) silicones, and may cause warpage in the display panels because of shrinkage on curing.
Under such circumstances, objects of the present invention are to provide a polyimide silicone resin which can form films at relatively low temperature, has superior adhesiveness to substrates and durability under conditions of high humidity and also has low stress and high elongation, to provide a polyimide silicone resin solution composition used to form films, and to provide a polyimide silicone resin film which may cause neither warpage nor copper sheet corrosion when used in electrode protective films for electronic component parts or semiconductor devices.
As a result of extensive studies, the present inventors have discovered that a polyimide silicone resin derived from a diamine comprising a diaminopolysiloxane and an acid dianhydride, which comprises at least 50% by weight of a siloxane residual group, and has an elongation at rupture of 400% or higher and a modulus of elasticity of 500 N/mm2 or lower, its solution composition and a film comprised of the composition and formed on a substrate, can achieve the above objects. Thus, they have accomplished the present invention.
That is, the present invention in the first aspect provides a polyimide silicone resin derived from a diamine comprising a diaminopolysiloxane and an acid dianhydride, which comprises at least 50% by weight of a siloxane residual group, and has an elongation at rupture of 400% or higher and a modulus of elasticity of 500 N/mm2 or lower.
The present invention in the second aspect provides a polyimide silicone resin solution composition comprising the above polyimide silicone resin and a ketone solvent having a boiling point of 130xc2x0 C. or below.
The present invention in the third aspect provides a polyimide silicone resin film comprising the above polyimide silicone resin and formed on a substrate.
The present invention will be described below in detail.
The polyimide silicone resin is obtained from a diamine comprising a diaminopolysiloxane and an acid dianhydride.
The acid dianhydride which may be used for the polyimide silicone resin of the present invention includes, e.g., 4,4xe2x80x2-hexafluoropropylidenebisphthalic dianhydride (6FDA), 3,3xe2x80x2,4,4xe2x80x2-diphenylsulfonetetracarboxylic dianhydride, 3,3xe2x80x2,4,4xe2x80x2-biphenyltetracarboxylic dianhydride, 4,4xe2x80x2-benzophenonetetracarboxylic dianhydride, and ethylene glycol bistrimellitic dianhydride. In particular, 6FDA and 3,3xe2x80x2,4,4xe2x80x2-diphenylsulfonetetracarboxylic dianhydride are preferred. Any of these may be used alone or in combination of two or more types.
The diamine which can used for the polyimide silicone resin of the present invention preferably includes, in addition to the diaminopolysiloxane, e.g., diamines represented by the general formula (2): 
wherein X represents xe2x80x94C(CH3)2xe2x80x94, xe2x80x94C(CF3)2xe2x80x94 or xe2x80x94SO2xe2x80x94. The diamines represented by the general formula (2) includes 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, and bis-4-(4-aminophenoxy)phenylsulfone. Any of these may be used alone or in combination of two or more. In particular, 2,2-bis[4-(4-aminophenoxy)phenyl]propane is preferred.
As the diaminopolysiloxane used in the polyimide silicone resin of the present invention, compounds represented by the following general formula (1) are preferred, any of which may be used alone or in combination of two or more types. 
wherein n represents the number of repetition of dimethylsiloxane unit, and is an integer of 0 or more, preferably 0 to 120, and more preferably 0 to 90.
The siloxane residual group in the present invention is meant to be a group represented by xe2x80x94(R)2SiOxe2x80x94 where R represents an alkyl group such as methyl, ethyl, propyl, phenyl groups, and the content of the siloxane residual group can be determined according to the following expression for calculation.
Siloxane residual group content (% by weight)=(weight of siloxane residual group calculated from the weight of the diaminopolysiloxane used)/(weight of polyimide silicone resin to be produced theoretically from the weights of the raw materials used)xc3x97100
In the polyimide silicone resin of the present invention, the siloxane residual group is in a content of 50% by weight or more, and preferably from 55 to 75% by weight. If it is in a content less than 50% by weight, the resin may cause a great shrinkage on curing.
The polyimide silicone resin of the present invention has an elongation at rupture of 400% or higher. It also has a modulus of elasticity of 500 N/mm2 or lower, and preferably 100 N/mm2 or lower. If it has an elongation at rupture lower than 400% or a modulus of elasticity higher than 500 N/mm2, the resin may cause distortion such as warpage in the panel after it has been formed into the polyimide silicone resin film.
In the present invention, the polyimide silicone resin may preferably less contain a cyclic siloxane oligomer having 20 or less silicon atoms. The cyclic siloxane oligomer having 20 or less silicon atoms is represented by the formula:
[(CH3)2SiO]n
wherein n is an integer of 3 to 20. For example, when n is 3, it is hexamethylcyclotrisiloxane and, when n is 4, octamethylcyclotetrasiloxane. These cyclic siloxane oligomers are volatile, and are known to cause what is called silicone trouble, such as trouble in electrical contacts. Accordingly, where the resin is used for electric and electronic purpose, these cyclic siloxane oligomers may preferably be in a content as small as possible. In order for the resin not to cause this silicone trouble such as trouble in electrical contacts, such volatile silicones in the polyimide silicone resin may preferably be in a content not more than 300 ppm, and more preferably not more than 100 ppm.
As solvents used in the present invention to obtain the polyimide silicone resin solution composition, there are no particular limitations thereon as long as the solvent can dissolve the polyimide silicone resin. Preferably, the solvent may preferably be a ketone solvent having a boiling point of 130xc2x0 C. or below. The ketone solvent having a boiling point of 130xc2x0 C. or below may include, e.g., acetone, 2-butanone and 4-methyl-2-pentanone.
In the present invention, the polyimide silicone resin can be produced by any known process. For example, a preferable polyimide silicone resin can be produced in the following way.
In an atmosphere of an inert gas, an acid dianhydride, e.g., 4,4xe2x80x2-hexafluoropropylidenebisphthalic dianhydride (6FDA), a diaminosiloxane, and optionally a diamine other than the diaminosiloxane, e.g., 2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) are charged into a solvent such as cyclohexanone to allow them to react at a low temperature, i.e., at about 10 to 50xc2x0 C. to synthesize a polyamic acid which is a precursor of the polyimide resin.
Here, the ratio of the diamine comprising the diaminopolysiloxane to the acid dianhydride may be in the range of from 0.95 to 1.05, and preferably from 0.98 to 1.02, in molar ratio. Also, the proportion of the diaminopolysiloxane in the diamine component may be from 0.7 to 1.0.
Subsequently, the resultant polyamic acid solution composition is heated to a temperature usually in the range of from 100 to 200xc2x0 C., and preferably from 140 to 180xc2x0 C., to cause the acid amide moiety of the polyamic acid to undergo dehydration cyclization reaction to obtain the polyimide silicone resin in the form of a solution composition. Here, toluene, xylene or the like may be added for the purpose of azeotropic dehydration to accelerate the dehydration cyclization.
As a solvent which may be used when the polyimide silicone resin of the present invention is synthesized, it may preferably be a non-reactive solvent capable of dissolving the polyimide silicone resin to be formed. Such a solvent may include, e.g., N-methyl-2-pyrrolidone, xcex3-butyrolactone and N,N-dimethylacetamide.
The polyimide silicone resin thus obtained may have a weight-average molecular weight (in terms of polystyrene) of from 5,000 to 150,000, and preferably from 10,000 to 100,000, as measured by gel permeation chromatography (GPC).
The polyimide silicone resin solution composition of the present invention may be coated on a substrate such as a metal sheet or plate, a glass sheet or plate, a ceramic substrate or a silicon wafer by a known process such as spin coating, dipping or potting. Thereafter, the coating formed may be dried under conditions of a temperature of from room temperature to 100xc2x0 C. during a few minutes to a few hours, thus the polyimide silicone resin film can be obtained with ease. The polyimide silicone resin film of the present invention has superior mechanical properties and electrical properties, and hence is preferably usable as an electrode protective material for electronic component parts or semiconductor devices. Stated specifically, it is preferably usable as an electrode protective film for TFT liquid-crystal display panels, STN liquid-crystal display panels or plasma display panels, as a junction film for ICs and as a conformal coating of printed circuit boards.